1. Field of the Invention
The present invention is related to a kind of vertical electrode structure of GaN-based light emitting diode. The GaN-based light emitting diode especially refers to a kind of diode with vertical electrode structure, which can effectively reduce Fresnel refraction loss and the total reflection, and further advance the external luminous efficiency.
2. Description of the Related Art
Accordingly, the application purpose to study the blue light emitting diode is to manufacture the full-color display, traffic light, and luminescent source. Nowadays, the prevailing various light emitting diodes in the market so far are with a variety of lights including red, green, orange, and yellow lights. However, as to the blue and green light emitting diodes, the practical degrees of high efficiency and high luminescence degree are still in development. And if the InGaN, GaN, and AlInGaN can be used as basic materials combined with the already matured development of red light emitting diode to make the blue light and green light emitting diodes with high luminescence, it can achieve the purpose to produce the full-color display. In addition, the present used traffic signals of lamp have the failures of energy consuming, short life, and the phantom image of illuminating (which occurs as the sunlight reflects off the display surface and easily causes the traffic accident). Hence, if the conventional lamp can be substituted with the red, blue, and green light emitting diodes of high luminescence, it can enhance the visibility of the traffic lights significantly. The slightly improved blue light emitting diode technology can further constitute the blue light semiconductor laser, and the short wavelength blue-violet light semiconductor laser can be utilized to replace the red light semiconductor laser (optical pickup head) used in the present disk so as to increase the recording capacity of the disk at least 3 times. In other words, it is exciting that in the future, the disk with the diameter of 12 cm can bear the motion pictures of at least 3 hours. With the blue light emitting diode combined with the yttrium-aluminum-garnet fluorescent material, the blue light can be utilized to ignite the yellow fluorescent material so as to produce the yellow light, and some of the blue light would also be emitted out at the same time and mixed with the yellow light together into the white light. As the white light emitting diode has many advantages including long life, energy saving, low driving voltage, safety, and environmental conservation, it has been regarded as the light source of twenty-first century. In addition, the GaN can also be formed as UV light emitting diode with the light of short wavelength, which is affiliated to the light of high energy and can be applied into medical care, food treatment, greenhouse growing, and etc.
In the conventional technology—the GaN-based light emitting diode made of sapphire substrate—as the substrate is not conductive, it is necessary to make the lateral electrode structure. As shown in the FIG. 1, wherein the included sapphire insulating substrate 100′ is epitaxized subsequently with a buffer layer 110′ a N-type semiconductor layer 120′, a light emitting layer 130′, a P-type semiconductor layer 140′, a first electrode 145′, and a second electrode 122′. Besides, in the conventional art, the silicon carbide can also be adopted as the substrate of GaN-based light emitting diode. Although the silicon carbide substrate with the conductive characteristic can be made into vertical electrode, the manufacturing cost is very expensive. Therefore, until now, the insulating substrate is dominantly utilized to manufacture the GaN-based light emitting diode. However, it has to make the lateral electrode structure if adopting the insulating substrate, which contributes the unavailability of the vertical electrode. This being the case, it would take the special wire bonding apparatus and packing technology, and additionally, the manufacturing area of chip will also increase relatively, thus complicating the manufacturing process and increase the cost of each component.
As the disclosed patent of No. 480740 in Taiwan patent gazette, from FIG. 2A to FIG. 2C, the first conductive lower cladding layer 210′ is formed on the first substrate 200′ and then the second conductive upper cladding layer 220′ is formed next to the upper lower cladding layer 210′. Then form an ohmic contact layer 230′ on said upper cladding layer 220′, and construct a reflection layer 240′ on said ohmic contact layer 230′. Subsequently, bond a second substrate 250′ on said reflection layer 240′ and remove the first substrate 200′, and then fabricate the first electrode and second electrode which are capable of conductivity to said upper cladding layer 220′ and lower cladding layer 210′ separately. Such kind of manufacturing process of light emitting diode, which is applicable of adopting insulating substrate directly, facilitates the manufacturing of the light emitting diode with vertical electrode.